They must have an allowance for each house?

Serena mentioned a cosmetic in their gift bag cost $200. Tristan and Bec said they got new furniture for their houseboat. This suggests the producers gave each pair a sum to upgrade their house before their guests arrived. Each pair chose how they would spend that money.

I think it would have been more interesting if the viewing audience had been made aware of how much and what it was spent on.

More allowance money for the finals?
It seemed like the owners who were in the finals were given additional funds to make changes to their space for the finale. Both homes had expensive upgrades in a very short amount of time (according to Ashfield).

I suspect that’s the only reason why someone like Anita would get involved in a cheesy reality tv show like this. Their house was beautiful. Making it to the finals probably netted them the cash they needed to finish the outdoor upgrades.

Also, the exposure was great advertising. Most of the teams likely benefited from that.

Edited to add:
In s2 they announced before the finals that they were giving each finalist $10K to upgrade their home. I’m glad they announced it as it makes it much more interesting.